1. Field of the Invention
The present invention relates to the field of processes for synthesizing or otherwise forming and growing single crystalline beryl, and more specifically, to a unique process which utilizes specific fluxes and specific method steps of heating and cooling the molten salt used to form the beryl crystals.
2. Prior Art
Recently there has been an increased demand for synthetic beryl which has found its application in gemstone members represented by emeralds. Moreover, aside from the aesthetic quality of the emeralds in jewelry and the like, synthetic beryl has also been used in microwave device members and other industrial devices. Among the processes heretofore introduced for synthesizing the beryl are a hydrothermal process and a molten salt process which utilizes a flux.
The molten salt process has a distinct advantage over the hydrothermal process in that the molten salt process saves considerable working energy in the form of heat and pressure which are otherwise required for the growing of the crystals under the hydrothermal process. Moreover, the molten salt process also simplifies the type of apparatus used to grow the crystals. The molten salt process is also far simpler than the hydrothermal process from the point of view of synthesizing procedures in that the hydrothermal process requires a hydrothermal reaction effected by maintaining an autoclave of complicated structure at high temperatures and pressure for a long period of time.
In the molten salt process, synthetic beryl are grown around beryl seed crystals by adding a flux to the beryl component oxides. The mixture is then heated at a temperature higher than that at which the fluxes are melted thereby forming the mixture into a molten salt. Beryl seed crystals are then placed in a molten salt while continuing with either of two heating procedures; in a first prior art embodiment the molten salt is maintained at a definite temperature range of a long period of time during which the growth of the beryl takes place. The other procedure is one in which the liquid i.e., the molten salt is cooled after having maintained the salt at a definite temperature for a certain period of time.
In this manner, the molten salt process makes it possible to form and grow single crystalline beryl by merely inserting seed crystals into the molten salt, heating the salt and maintaining the heating temperature for a comparatively short period at a temperature higher than the melting point of the flux, normally at a temperature range of 700.degree. to 1,050.degree. C.
Nevertheless, this molten salt process leaves the following problems yet to be solved:
1. The amount of beryl of high purity is small for the amount used in one batch of component oxides of the beryl. Namely, according to the molten salt process of the prior art, formation conditions for beryl formed and grown around the seed crystals are very unstable both in quality and quantity. This is thought to be due to the fact that paragenic materials such as green beryl (BeAl.sub.2 O.sub.4), phenacite (Be.sub.2 SiO.sub.4) and other crystobalite (SiO.sub.2), etc. are likely to be formed in high percentages. It also happens not infrequently in an extreme case that paragenic materials are grown or produced and no beryl at all comes out. What is considerd the cause of this is that a change of intercombination of components BeO, Al.sub.2 O.sub.3, and SiO.sub.2 in the component oxides of beryl do not form the desired composition of beryl of three component types of BeO .multidot. Al.sub.2 O.sub.3 .multidot. 6SiO.sub.2 but forms two component types of BeO-Al.sub.2 O.sub.3 (chrysoberyl) and BeO-SiO.sub.2 (phenacite) or a single component type of SiO.sub.2, depending upon the temperature of the molten salt. This is thought to be because the mineral-based substances combined and formed follow the order of stability in the temperatures of the substances. That is, it is considered that the cause seems to lie in the fact that chrysoberyl and phenacite are more predominantly stable, for example, in the neighborhood of the upper limits of the stable temperature sphere of formation of beryl and that chrysoberyl and phenacite are predominantly formed prior to the formation of beryl. Beryl, therefore, comes out later in order. This tendency has been more conspicuous in such a case as that of synthetic emeralds which contain a coloring component. It may also be said that in the prior art processes no idea has ever been proposed of systematically tackling these problems discussed hereinabove in connection with mineral substances formed from a molten salt and of producing beryl predominantly and effectively from the molten salt.
2. Seed crystals obtained from natural beryl had to be used for industrially producing beryl. Although beryl is formed without seed crystals, the amount of beryl formed as described hereinabove, is highly unpredictable. Therefore in order to realize reproducibility, recourse was had to the growth of seeds as an indispensable condition for forming synthetic beryl.
The present invention represents an advance in the art of beryl production and contains none of the aforementioned shortcomings associated with prior art methods. Moreover, the need for seed crystals is eliminated.